Polyamides are generally produced by ring open polymerization of lactams effected by melt bulk polymerization, solid bulk polymerization, or suspension polymerization or precipitation polymerization using organic media.
According to the suspension polymerization technique, a lactam is suspended in an organic suspending medium in which the lactam is insoluble or sparingly soluble in the presence of a suspending agent and polymerized using an anionic polymerization catalyst and a polymerization activator.
Japanese Patent Publication No. 10636/61 discloses a process for polymerizing various lactams suspended in a paraffin oil or a silicone oil with the aid of a polyaminocaproic acid powder or talc as a suspending agent in the presence of an alkaline catalyst and a polymerization activator such as an isocyanate, a carbodiimide, a cyanimide, etc.
Japanese Patent Publication No. 42719/73 discloses a process for polymerizing 2-pyrrolidone using a nonionic surface active agent as a suspending agent and N-acetylpyrrolidone, isocyanates, carbon dioxide, etc. as a polymerization initiator.
Japanese Patent Publication No. 4837/74 discloses a process using a homo- or copolymer of an olefin or diolefin having a molecular weight of at least 1500 as a suspending agent.
Processes for producing polyamide block copolymers by the solid bulk polymerization technique are disclosed, e.g., in U.S. Pat. Nos. 3,862,262 and 4,540,515, European Pat. Nos. 67,693 and 147,051, etc.
Homopolymers of lactams obtained by the conventional suspension polymerization techniques were unsatisfactory in flexibility, impact resistance, and the like. The bulk polymerization techniques provide copolymers but require extra special devices or operations for obtaining copolymers in the form of granules or powders easy to handle.